2 Speed Tranny Idea

[mclovin]

Hi All,
Maybe this has been tried before. I don't know.

 

[Miles]

It's in here somewhere, I think

http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=8644

 

[mclovin]

It looks like it's being used in a little scooter of some sort. That means it works, I wonder how well though?

Here's the same idea in a better packaging configuration.

I would expect this to be very cheap to fabricate (purchased parts not withstanding). The side plates could be made by many different methods from flat sheet/plate using CNC laser, router, mill, water jet. In volume production the plates could be re-engineered to be extruded......A thought.

 

[Miles]

I like that one.

It was also discussed here:
http://www.endless-sphere.com/forums/viewtopic.php?f=10&t=9695

 

[spinningmagnets]

I'm not sure a centrifugal clutch would work well in this application (I don't know, just guessing). But I'm certain the common plate-style of clutch (whats the proper name?) would work well, but actuated by a stick-shift instead of a spring-return lever (high-range/low-range).

For the freewheel, I have been reading about one-way bearings by CSK. They are made in many sizes, and some are quite beefy. Small enough for an E-bike, and others big enough for an E-motorcycle. I just found out they are commonly found on washing machines. There is a linkage that allows it to agitate back-and-forth, and another linkage that spins the tub dry. Washing machines have an electrically-actuated clutch (I adjusted a slipping one once, to get it to last another month while I shopped for a new washer)

They spin freely in one-direction, and grip well in the other, capable of handling a lot of torque quietly and smoothly. BTW...GREAT graphics, mclovin!

http://www.marland.com/products/sprag/sprag-csk.html

 

[Miles]

CSK is the series classification. I used a CSK 35 on my Moulton conversion.

 

[spinningmagnets]

Here is a link from a Dutch site about the history of Mopeds in the 1950's. Immediately after WWII, single-speed 2-strokes caught on because of their simplicity and low-cost. You could pedal when alone to save on expensive (and sometimes unavailable) fuel, and use the gasoline engine when hauling cargo. As many of you know, the Netherlands are very flat, and it is famously bike-friendly.

http://www.veteranknallert.dk/0200/eng_0211.htm

One of the first upgrades consumers wanted when they could afford it were more gears, and although later models evolved into light motorcycles, the early 50's saw a variety of well-engineered 2-speed systems. I find the planetary 2-speed to be interesting...

http://www.veteranknallert.dk/0200/eng_0222.htm

 

[12p3phPMDC]

Spinning Magnets,

That planetary is the way to go IMHO!Thanks for posting that link!

But who cares about transmissions....the best stuff on that site is this:



View attachment 1

 

[mclovin]

A manually activated friction type clutch would be prfereable. Engaging a passive, centrifugal clutch may slow the motor enough to cause the clutch to release (I guess). It seems to work in non-ebike applications so I imagine it will work with the proper "engineering" of motor, gear ratios etc. A manually engaged clutch, however, eliminates any risk. My first thought would be how much does a manual clutch cost? Those go-cart centrifugal clutches run less than $30 but would need some modification to fit our needs (shaft size reducer, tuning engagement RPMs, perhaps changing the sprocket).

http://www.mfgsupply.com/m/c/4-455.html?id=oILXV4ZM
http://www.maxtorque.com/html/clutches.html

So I recon the true cost may be around $70 or so. But if #35 chain, 2200RPM engagment and a 3/4" shaft are OK then $30 will do the trick.

Anyone know where to find a manual clutch?

 

[mclovin]

A slightly more compact arrangement.

The motor could be mounted on either side and the clutch could be too.

 

[12p3phPMDC]

Is the transmission in 1st gear until the clutch engages at a certain speed
shifting into second?
i.e. the shift point adjusted by counterweights.

 

[Miles]

Is the transmission in 1st gear until the clutch engages at a certain speed
shifting into second?

Yes. That's right.

 

[12p3phPMDC]

Thanks Miles.

I like the retro-direct concept, it's like a relay team with
a fat guy who is really strong but can pull you up a hill and a skinny sprinter who
can run really fast on the flats but if you load em down he's worthless with centrifugal clutch as the baton.

But, I just have this damn obsession with planetaries.

 

[spinningmagnets]

The EVO-2 is a 40cc stand-up scooter. This 2-speed trans has been mentioned in another thread (thanks, Miles), but it might have some good ideas for the current discussion. 49/50cc's seems to be a licensing/insurance/registration limit in some juristictions, so the added performance of the 2-speed tranny might be worth the extra cost to some..

 

[spinningmagnets]

At the other end of the scale, there are RC cars now using gasoline engines such as the TRX 3.3cc (roughly a nickel-sized piston diameter) and one of the upgrades is a 2-speed transmission. Even if the biggest RC trans is still too small for a 500W E-bike motor (or not as strong or as cheap as a 3-speed bike hub) there might be some useful engineering ideas, as these clearly do work.

Also, they all seem to use the combo freewheel bearing/centrifugal clutch. I have been idly skimming info on clutches from washing machines, tillers, and ICE engine radiator fans...

(in reviewing older threads on this, I want to credit Miles and Frodus for giving me some of these ideas, thanks!)

TGN hpi Baja 5b

2042 Nitro TC3 RTR

Traxxas

 

[12p3phPMDC]

I agree that a manually thrown clutch would be better.
But that means you have to run a cable or lever and an actuator...
Automatic operation is nice in that regard.
The only experience I have with centrifugal clutches are with my chainsaw.

How would you tune the "lock up" speed....new springs...new weights?

As far as 50cc being a limit before hitting regulation, just run a small
can of NOS or build an electric supercharger....

 

[lawsonuw]

A slightly more compact arrangement.

The motor could be mounted on either side and the clutch could be too.

A good looking design overall. I'd personally make two changes. First I'd move the centrifugal clutch to the output shaft. This will make the shift point of the transmission dependent on ground speed instead of motor speed. Second I'd try to modify the clutch to have as aggressive engagement as I could manage. (flipping the shoes arround, playing with spring configurations, and weights. I'm pretty sure the RC trannies show integrate both of these ideas)

Lawson

 

[mclovin]

How would you tune the "lock up" speed....new springs...new weights?

New springs for sure. Maybe weights too. I'm not sure what the clutch mfg. has in the way springs. I saw a few different sets on their website but I don't know if they fit the $30 clutch. I will need to contact them and find out more.

 

[John in CR]

I have plans in the works for a similar 2 speed, but using an electromagnetic toothed clutch. Ideally I want to find one that engaged is the unpowered state, which will probably require one designed for use as a brake in the event of power failure. That way no juice is required for 2nd gear, and I expect that 2nd gear is where the most time is spent, so 20W or so to activate the disengaged status for 1st gear will more than pay for itself with better efficiency at lower speeds and higher torque, especially on hills. I like the idea of positive engagement with a toothed clutch that can handle lots of torque in a very compact and durable package, and changing gear is done with just the flip of a switch (and let off the throttle to avoid a jerk upon engagement, just like ICE manual shifting).

John

 

[12p3phPMDC]

I agree that toothed clutch is the way to go. A magnetic clutch with a spring return would be nice.
As you can see in the 2 speed planetary picture, the designer used small teeth when the sun gear is locked to the
planet carrier to lock the planetary assembly at 1:1. Anytime you lock any two of gears of a plantary it locks the assembly.
It then uses a tooth clutch on the other end of the stroke for 1st gear.

Sturmey archer internal gear hubs do the same thing as the moped tranny and it looks like they have tooth clutches as well.
The three speeds have an additional set of planets.

I can't wait to run the Nexus3 e-trans tied to the Nexus8 human-trans!! That will be planetary heaven with the
moped women if my LiPos blow up! :lol:

 

[John in CR]

I can't wait to run the Nexus3 e-trans tied to the Nexus8 human-trans!! That will be planetary heaven with the
moped women if my LiPos blow up! :lol:

I'm not sure what you mean here, but back in the day we used to call some girls "mopeds". Just like a moped they were fun to ride, but you just didn't want your friends to see you on one? Now that E-geeks get all the girls, I guess you have a different meaning.

John

 

[Miles]

I like the retro-direct concept.............
But, I just have this damn obsession with planetaries.

You can have both together.....

If you lock the planet carrier and use the sun for input and the ring for output, with a few overrunning clutch bearings, you have a retro-direct epicylic

 

[12p3phPMDC]

Well, you know what they say, never pass one up! ....hhggmm....a good moped or e-bike that is...

The joke is a bad reference to suicide bomber and the women waiting for him on the other side.

Hmm....retro direct epicyclic. I'll have to sleep on it! **confused***

But, I can envision a tight package.

 

[Miles]

Hmm....retro direct epicyclic. I'll have to sleep on it! **confused***

This configuration (locked planet carrier) reverses the drive direction so, in alternation with a completely locked state (1:1), you get the possibility for retro-direct operation.

 

[mclovin]

I'd personally make two changes. First I'd move the centrifugal clutch to the output shaft. This will make the shift point of the transmission dependent on ground speed instead of motor speed. Second I'd try to modify the clutch to have as aggressive engagement as I could manage. (flipping the shoes arround, playing with spring configurations, and weights. I'm pretty sure the RC trannies show integrate both of these ideas)

Lawson

Yes, placing the clutch on the output shaft is an alternate configuration that has its advantages. As long as the different engagement speed is taken into account (springs, weights) and that a lager sized sprocket can be fitted it should just fine. However if the user configures their setup as a through-crank design then the freewheel in the crank would eliminate ground speed input and again the engagment would be "set" by the motor. If the design is applied in a "direct" drive (i.e. a left hand fixed sprocket on the rear wheel) then wheel speed would, as you pointed out, determined the engagement of the clutch.

I do wonder about the engagment type, though (aggressive engagment vs. smooth engagment). A shock type engagment may result in a big CLUNK feel when shifting and be a bit off-putting to the rider. A smooth engament "MAY" be more beneficial in that it gradually adds input from the clutch ergo smoother shifting and a better "feel." But I could be totally wrong.

In either case the motor will need to be sufficient enough to deliver the torque/speed needed into succesfully transition to high gear. I personally don't know how to characterize motor response when the load changes so in that area I draw a bit of a blank (motor gurus please feel free to chime in). I think that the transient response of the motor is likely the key factor in determing successful shifting performance for this VERY low cost centrifagul design.

If more money can be spent by the DIY ebiker then a positive engagement clutch would be a dandy solution. I'd be interested in seeing what types of variable engagement magnetic clutch designs are out there. A variable clutch engament may prove to be effective for ebike gearing if the prices are affordable.

IMO the "best" solution will be linked to how much money we can spend. As for me, I'm on a pretty tight budget so I'm gravitating this centrifagul design. Hopefully it pans out. :wink: